Thanos Papanicolaou
IIHR - Hydroscience & Engineering, The University of Iowa

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Application Note: Hydraulic Structures
 
Design and evaluation: Hydraulic structures are typically used for flood control, flood conveyance, irrigation purposes, fish passage, banks protection, navigation, recreation and ecological restoration.   A hydraulic structure must meet the safety, functional and aesthetic goals for its purpose.  Thus, valuation studies must be carried out before and after the construction of the structure to assess its impacts. The structure must be of sufficient size that natural flooding is not worsened and to ensure that the structure can withstand the design flood and remain traversable.  This is required in order to protect the property and residents upstream and downstream of a structure.  In the hydraulic design, one main thing to remember is that water is dynamic.
   
 

Black Lake restoration:  The water storage capacity of Black Lake, Alaska has decreased over the past 55 years. This reduction had detrimental effects on fish species in the region.  In the last three years, commercial fishery production has declined from an average of 1.56 million (1994-2003) to 0.91 million (2004-2006) harvested sockeye salmon, a loss of nearly 0.65 million sockeye salmon.  A study was conducted to identify the possible hydrologic and geomorphologic changes causing the reduction of the Black Lake water storage capacity, propose the remedial action required for the lake to regain its original storage capacity, and predict changes in the lake’s boundaries, storage volume, and water surface elevation for different flow conditions.  The findings of this research suggested that the lake receives sufficient water influx to maintain its maximum storage capacity.  Moreover, sedimentation was found not to be an issue, because siltation since 1950 has reduced the storage capacity by only 1.0 %.  The reduction in the lake storage was attributed mainly to changes of the outlet geometry of the lake.  Field measurements revealed that the outlet elevation of the lake has decreased by at least 1.0 m since 1950 due to severe degradation.  For remediation, a routing model simulated different flow events to determine the optimum lake outlet elevation needed for the lake to regain its original storage volume.  This study recommended that a gated weir can be used as a control structure to maintain the elevation at the lake’s outlet.  In addition, an erosion model predicted that the lake may loose 80 % of its current storage capacity within a 100-year period assuming that the current climatic conditions are present and no remedial action is taken.